PURPOSE: To carry out lead wire connection work in a tank for in a short period and also remove danger of generating metal foreign matter in the tank by a method wherein high voltage lead parts inside a device are mutually connected by using insulation supplementary means molded in advance.

CONSTITUTION: High voltage lead parts inside a device are mutually connected via a connection adapter 10 made outside the tank in advance. In addition, a filler and a sheet foil are not used unlike the prior art and a thickness of a winding insulation tape 12 is extremely thinned and an extending barrier 11 prepared outside the tank in advance is used instead. Thus, a working period for performing the winding insulation tape being an insulation cover can be reduced as compared with the prior art, and also a generation of metal foreign matter can be avoided.